Zondervan, Edwin

University of Groningen

   University of GroningenIntermediate to long term optimization of dead-end ultrafiltrationZondervan, EdwinIMPORTANT NOTE: You are advised to consult the publisher's version (publisher's PDF) if you wish to cite fromit. Please check the document version below.Document VersionPublisher's PDF, also known as Version of recordPublication date:2007Link to publication in University of Groningen/UMCG research databaseCitation for published version (APA):Zondervan, E. (2007). Intermediate to long term optimization of dead-end ultrafiltration. s.n.CopyrightOther than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of theauthor(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons).Take-down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediatelyand investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons thenumber of authors shown on this cover page is limited to 10 maximum.Download date: 12-11-2019Chapter 4Characterization of membranefoulingIn this chapter results of an autopsy performed on a PES (Poly Ether Sul-phone) ultrafiltration membrane that was operated with surface water in apilot over a six month period are presented. The outcome of the membraneautopsy showed that fouling present on the membrane surface is a complexmixture of polysaccharides, silica, organic industrial or urban waste such asalkyl-benzenes, phtalates and plant materials. By studying feed, permeate,backwash concentrate and cleaning concentrates during the operation periodof the pilot, it could be concluded that especially silica, iron and organic con-tent, tested as DOC (Dissolved Organic Content) and TOC (Total OrganicContent) are retained on the membrane surface. This is in good agreementwith the autopsy data.4.1 IntroductionBetter understanding of fouling may lead to improved fouling preventiontechniques [1; 2]. The main objective of this chapter is to determine, in aqualitative way, which surface water components are retained on the mem-brane surface and cause fouling.As stated in chapter 2, surface water can basically be divided into threetypes of potential fouling categories: 1) organic content, 2) inorganic con-tent and 3) microbial content. Sometimes a fourth category may be added:5960 CHAPTER 4. CHARACTERIZATION OF MEMBRANE FOULINGcolloidal content. The organic content of surface water is often addressed asNOM (Natural Organic Matter) which is the collective name for humic- andfulvic acids. Several studies [3; 4; 5; 6; 7; 8] have shown that interactions,such as physical bridging and electro-static (van der Waals) repulsion occurbetween organic content and inorganic content (metal ions) and contributesignificantly to membrane fouling. However, other work [10; 11] shows thatmicrobial activity may result in membrane fouling, as microorganisms at-tach to the membrane surface and secrete extra cellular poly saccharides,forming a protective layer around the microorganisms.4.2 Materials and methods4.2.1 The 4 Inch ultrafiltration pilotIn this research a 4 Inch Norit-Xiga PES ultrafiltration module with a mem-brane surface of 6.0 m2 was operated over a six month period. Surfacewater was pre-treated with a 200 micron pre-filter, before it was processedin the pilot setup. Pre-filtered feed water was filtrated in dead-end modeover the membrane module with an operating flux of 50 l.h.−1.m−2 during20 minutes. During filtration, flocculant was added to the feed water witha concentration of 1.0 ppm Al3+ (Quadrafloc PUS, ViVo Chem B.V.). Af-ter a filtration run, a backwash was performed at an operating flux of 200l.h−1.m−2 during 2 minutes. When the trans-membrane pressure exceededan upper limit of 0.3 bar, the membrane was cleaned by means of chemicals.First the membrane was cleaned with hydrochloric acid ( 0.1 mol.l−1), fora period of 5 minutes flushing and 5 minutes soaking. In a second cleaningstep a caustic cleaning with sodium hydroxide ( 0.1 mol.l−1) was performed,flushing and soaking also lasted 5 minutes. The trans-membrane pressureand temperature were measured with pressure- and temperature indicators,filtration flux and backwash flux were regulated with pumps and flow con-trollers. The setup was connected via an interface (National Instruments) toa personal computer which was used to collect operational data. MEFIAS(Vito, Belgium) software was used to control the pilot. In figure 4.1 a sim-plified representation of the setup is presented. A photographic view of thepilot can be seen in figures 4.2 and 4.3.4.2. MATERIALS AND METHODS 61PT FF TPTPTP200 micronPre-filterStirredfeed tankFlocculantdosing tank(~1 ppmAluminium)4" Membrane modulePermeate tankChemicals tank(HCl ~0.1M)Chemicals tank(NaOH ~0.1M)Figure 4.1: Simplified representation of the 4 Inch Pilot setup.4.2.2 CharacterizationTwo sample sessions were performed during operation of the pilot (A fourweek period between both sample sessions), where feedwater, permeate,backwash concentrate and chemical cleaning concentrate (acidic- as wellas caustic) were analyzed at the Vitens Laboratory for inorganic content(calcium, magnesium, silica, iron and aluminum, nitrate, nitrite, chlorine,ortho-phosphate, sulphate and ammonium), organic content (UV254, totalorganic content and dissolved organic content) and overall feed water quality(pH, turbidity and conductivity).To characterize the fouling, a membrane autopsy was conducted in collabo-ration with the Universite´ de Poitiers by means of FTIR, UV, C/N-analysis,pyrochromatography and thermolysis. The module was opened and twosample sets of fibers were cut out, one on the outside of the module and oneat the center of the module. Material was isolated from fouled membranefibers using sonication in MilliQ water, followed by lyophilisation. Part ofthe fibers were used for SEM photography at the Wetsus center for sustain-able water technology.62 CHAPTER 4. CHARACTERIZATION OF MEMBRANE FOULINGFigure 4.2: 4 Inch pilot setup, front view of the setup with in the center themembrane module and permeate tank at right hand side.4.3 Results and discussion4.3.1 AutopsySEM photographySEM-pictures of fibers are shown in Figure 4.4. Algae were found duringSEM photography, in the upper left figure a diatom is shown. Also bacteriawere present (lower left and center figure). The lower right figures showfouling deposited on the membrane surface. It is noted that the foulingappears to be loosely deposited on the surface, this could be due to dryingand heating of the fibers during the SEM photography.4.3. RESULTS AND DISCUSSION 63Figure 4.3: 4 Inch pilot setup, back view of the setup with chemicals dosingsystem and feed tank (in the back).Table 4.1: Carbon and Nitrogen content found on the fibers. (In 100 ml.milliQ waterDOC (mg.l−1) TN (kg.l−1) C/Nsample 1 3.81 +/- 0.08 0.04 +/- 0.01 95sample 2 0.22 +/- 0.02 0.03 +/- 0.01 6.6Carbon and nitrogen contentThe C/N ratio is a frequently used indicator to quantify the nature of thedeposit. It is well known that the higher the hydrophilic character of theNOM, the higher the nitrogen content and the lower the C/N ratio. TypicalC/N ratios range from 4 -5 to more than 20 progressing from hydrophilic tohydrophobic NOM fractions. The two isolates showed very different carboncontent, but similar nitrogen content, and consequently different C/N ratios.The possible difference in the data may be a result of the original locationof the fibers in the module, where one sample was taken at the outside ofthe module and one sample was taken at the center of the module.64 CHAPTER 4. CHARACTERIZATION OF MEMBRANE FOULINGFigure 4.4: SEM photographs of the membrane. (Magnifications of 75× to10.000×)High pressure size-exclusion chromatography (HPSEC) analysisIn figure 4.5 the HPSEC/UV spectrum is presented. The peak at t=6.5 mi-nutes corresponds to high molecular weight proteins and polysaccharides.The broader band between 8 and 10 minutes may correspond to the pres-ence of a higher proportion of high molecular weight structures. Both sam-ples show peaks at similar wavelengths. Also the peak heights are similar,indicating that similar quantities of the components were present in thesamples.FT-IR analysisFT-IR analysis can be used as a qualitative technique to identify foulingcomponents. Results obtained for the FT-IR analysis, shown in figure 4.6,clearly indicate the presence of silica (clay mineral) with the major band at1100 cm−1 associated with the one at 470 cm−1. The large silica band mayhave overlapped with the characteristic band of sugars (1000-1100 cm−1).4.3. RESULTS AND DISCUSSION 65Figure 4.5: HPSEC/UV-260 of isolated foulants.The band at 1650 cm−1 is also significant and again may indicate the pres-ence of proteinaceous material. The large OH stretch at 3400 cm−1 mayindicate adsorbed water as well as organic hydroxyl groups. Both samplesshow peaks at the same wavelengths, indicating good reproducibility.Figure 4.6: FT-IR spectra of the Twente Canal isolates.Pyrolysis GC/MSAt high temperature, natural biopolymers and synthetic polymers are de-graded to low-molecular-weight thermal decomposition products that arevolatile enough to be separated and identified by GC/MS. The recordedpyrochromatogram, shown in figure 4.7, is dominated by the presence of66 CHAPTER 4. CHARACTERIZATION OF MEMBRANE FOULINGbranched alkyl benzenes.Figure 4.7: Pyrochromatogram of the Twente canal isolate (total ion currentand m/z 91 chromatograms).Clay minerals, as found in the FT-IR analysis of the samples, accumulatedat the membrane surface and contained probably contaminated branchedalkyl benzenes which strongly adsorb onto their surface.Thermochemolysis GC/MSThe chromatogram of thermolysis of the fouling is shown in figure 4.8. Themajor observation in the thermo-chromatogram is that the Twente canal wa-ter incorporates heavier fatty acids up to C26. The presence of C15 iso andC15 anteiso fatty acids is a strong indicator of bacterial input. The longerchain fatty acids originate most probably from plant materials potentiallyadsorbed onto clay materials identified at the membrane surface. The pre-sence of propenoic acid confirms the presence of plant materials, for examplelignin derivatives in the fouling material. The peak for dimethyl phthalate4.3. RESULTS AND DISCUSSION 67reinforces the hypothesis of industrial and/or urban contamination of theTwente canal.Figure 4.8: Thermochemolysis - TMAH/GC-MS chromatograms of the hol-low fiber foulants (end). (Ar1: Benzaldehyde, 4-methoxy; Ar2: Trimethoxy-benzene; Ar3 Benzene 4-ethenyl-1,2-dimethoxy; Ar4: Benzoic acid, 4-methoxy, methyl ester; Ar5: Benzaldehyde, 3,4dimethoxy; Ar6: Benzene,1,2-dimethoxy-4-(1-propenyl); Ar7: Benzoic acid, 3,4-dimethoxy, methylester; Ar8: Benzene 1,2,3-trimethoxy, propenyl; Ar9: Ethanone,1-(3,4,5-trimethoxyphenyl); Ar10: Benzoic acid, 2,4,5-trimethoxy,methyl ester;Ar11: Dimethyl phthalate; Ar12: Benzene dicarboxylic acid dimethyl ester;Ar13: Benzoic acid methyl ester; Ar14: Propenoic acid, 3-phenyl, methylester; Ar15: Propenoic acid, 3-(4-methoxyphenyl); Ar16: Propenoic acid,3-(3,4-dimethoxyphenyl)).4.3.2 Laboratory analysis of feed, permeate and con-centrateFeed water, permeate, and cleaning concentrate (backwash, caustic andacidic) were sampled and analyzed. In figure 4.9 the results for feed wa-ter are shown.The concentrations of permeate, backwash concentrate and cleaning concen-trate are normalized by the concentration of the component present in thefeed water and shown in table 4.2.68 CHAPTER 4. CHARACTERIZATION OF MEMBRANE FOULINGFigure 4.9: Lab. analysis results for feed water before and after coagulantdosing (Poly aluminium chloride).From the permeate analysis it can be seen that especially turbidity, ortho-phosphate, aluminum and iron are retained on the membrane.During backwashing, especially turbidity, ortho-phosphate, aluminum andiron are removed from the membrane surface.From the analysis of acidic- and caustic cleaning concentrate it can be seenthat also other components are removed in large quantities, which impliesthat they were retained on the membrane surface.For caustic cleaning especially, nitrite, ammonium, silica, aluminum, ironand organic content (DOC and TOC) were removed, while during acidiccleaning ortho-phosphate, aluminum, iron and organic content (UV254) wereremoved. The high values for conductivity and chlorine can be explained bythe high chlorine content of the cleaning agent (Hydrochloric acid) itself.values for DOC and TOC are twice as high in the caustic cleaning concen-trate as found for the feed, implying significant presence of organic contenton the membrane surface. Also the increase in values for UV254 duringacidic cleaning indicates the presence of organic content.Aluminum and iron are present on the membrane surface, aluminum is de-posited on the membrane surface as it is dosed to the feed water as a floc-culant. Also silica is deposited on the membrane surface, most probably asa result of clay- or sand particles present in the feed.4.3. RESULTS AND DISCUSSION 69Table 4.2: Normalized analysis results for permeate, backwash concentrate,acidic cleaning concentrate and caustic cleaning concentrate.Permeate×FeedwatervalueBackwashconc.×FeedwatervalueAcidiccleaningconc.×FeedwatervalueCausticcleaningconc.×FeedwatervaluepH 1.01 0.99 0.30 1.43Conductivity (mS/m) 1.00 1.00 6.89 1.67Turbidity (FNU) 0.06 2.15 0.96 3.41UV254 (m−1) 0.96 1.04 1.74 1.46Nitrite (mg.l−1) 2.08 0.33 0.33 2.00Nitrate (mg.l−1) 0.94 0.98 0.86 0.95Chlorine (mg.l−1) 1.00 1.00 4.73 1.36Ammonium (mg.l−1) 1.00 1.00 1.40 6.80Ortho-phosphate (mg.l−1) 0.56 2.17 9.44 1.56Silica (mg.l−1) 1.00 0.97 1.33 2.35Sulphate (mg.l−1) 0.99 1.02 0.99 1.05Aluminium (µg.l−1) 0.10 2.08 7.22 2.02Calcium (mg.l−1) 1.00 1.01 1.01 0.90Magnesium(mg/l) 1.00 1.01 0.95 0.41Iron (mg.l−1) 0.02 1.76 1.85 3.45TOC (mg.l−1) 0.89 1.17 1.38 1.80DOC (mg.l−1) 0.95 1.14 1.70 1.93No tests were carried out for microbial content, however, the higher valuesfor nitrite and ammonium indicate that microorganisms might be presenton the membrane surface, converting nitrate into nitrite and ammoniumaccording to the nitrogen-cycle.70 CHAPTER 4. CHARACTERIZATION OF MEMBRANE FOULING4.4 ConclusionsThe results of the membrane autopsy showed that fouling present on themembrane surface is a complex mixture of polysaccharides, silica, organicindustrial or urban waste such as alkyl-benzenes and phtalates and plantmaterials. The analysis of feed water, permeate, backwash concentrate andcleaning concentrate support these results. Concentrations of indicatorsof organic content, such as TOC, DOC and UV254 are clearly higher inbackwash- and cleaning concentrate. Also iron and silica is found in higherconcentrations in the concentrates. Indirect prove for microbial activity isfound, as concentrations of nitrite and ammonia are evidently higher in thecleaning concentrates. During caustic cleaning, especially organic content isremoved, while during acidic cleaning inorganic content is removed.AcknowledgementsThe author would like to thank Dr. A. Zwijnenburg of the Wetsus Centerfor sustainable water technology for the SEM footage and Dr. Croue´ of theUniversite´ de Poitiers for the autopsy analysis data.BIBLIOGRAPHY 71Bibliography[1] Rabiller-Baudry M., Le Maux M., Chaufer B. Begoin L., Characterisa-tion of cleaned and fouled membrane by ATR-FTIR and EDX analysiscoupled with SEM: application to UF of skimmed milk with a PES mem-brane. Desalination, 146 (2002), 123-128[2] Maartens A., Jacobs E.P. and Swart P., UF of pulp and paper eﬄuent:membrane fouling prevention and cleaning. Journal of membrane science,209 (2002), 81-92[3] Yoon S.H., Lee C.H., Kim K.J. and Fane A.G., Effect of calcium ion onthe fouling of nanofilter by humic acid in drinking water production. Wat.Res., 32 (1998), 2180-2186[4] Li, C.-W. and Y.-S. Chen, Fouling of UF membrane by humic sub-stance: effects of molecular weight and powder-activated carbon (PAC)pre-treatment. Desalination, 2004. 170(1): p. 59.[5] Yuan, W., A. Kocic, and A.L. Zydney, Analysis of humic acid foulingduring microfiltration using a pore blockage-cake filtration model. Journalof Membrane Science, 2002. 198(1): p. 51.[6] Yuan, W. and A.L. Zydney, Humic acid fouling during microfiltration.Journal of Membrane Science, 1999. 157(1): p. 1.[7] Maartens, A., Swart P., and Jacobs E.P. , Feed-water pretreatment:methods to reduce membrane fouling by natural organic matter. Journalof Membrane Science, 1999. 163(1): p. 51.[8] Hong, S. and Elimelech M. , Chemical and physical aspects of naturalorganic matter (NOM) fouling of nanofiltration membranes. Journal ofMembrane Science, 1997. 132(2): p. 159.[9] Kang, S.-T., Subramani A. , Hoek E.M.V. Deshusses M.A. and Mat-sumoto M.R.. (2004). ”Direct observation of biofouling in cross-flow mi-crofiltration: mechanisms of deposition and release.” Journal of MembraneScience 244(1-2): 151.[10] Vrouwenvelder, J. S. and D. van der Kooij (2001). ”Diagnosis, predic-tion and prevention of biofouling of NF and RO membranes.” Desalination139(1-3): 65.72 CHAPTER 4. CHARACTERIZATION OF MEMBRANE FOULING[11] Weihua Peng, I. C. E., and White D.B., (2004). ”Effects of waterchemistries and properties of membrane on the performance and fouling-amodel development study.” Journal of Membrane Science 238(1-2): 33-46.

Intermediate to long term optimization of dead-end ultrafiltration

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Intermediate to long term optimization of dead-end ultrafiltration

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